The invention generally relates to a generator control system to accommodate a decrease in a power grid voltage.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:
H2xe2x86x922H++2exe2x88x92 at the anode of the cell, and
O2+4H++4exe2x88x92xe2x86x922H2O at the cathode of the cell.
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, multiple fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. Electrically conductive gas diffusion layers (GDLs) may be located on each side of each PEM to form the anode and cathodes of each fuel cell. In this manner, reactant gases from each side of the PEM may leave the flow channels and diffuse through the GDLs to reach the PEM.
A fuel cell system may include a fuel processor that converts a hydrocarbon (natural gas or propane, as examples) into a fuel flow for the fuel cell stack. For a given output power of the fuel cell stack, the fuel flow to the stack must satisfy the appropriate stoichiometric ratios governed by the equations listed above. Thus, a controller of the fuel cell system may determine the appropriate power that the stack needs to supply, and based on this determination, the controller estimates the fuel flow to satisfy the appropriate stoichiometric ratios to produce this power. In this manner, the controller regulates the fuel processor to produce this flow, and in response to the controller determining that a change in the output power is needed, the controller estimates a new rate of fuel flow and controls the fuel processor accordingly.
The fuel cell system may provide power to a load, such as a load that is formed from residential appliances and electrical devices that may be selectively turned on and off to vary the power that is demanded by the load. If the fuel cell system is producing more power than is being consumed by the load, then the fuel cell system may provide power to a power grid.
More than one fuel cell system may be connected to the power grid and thus, it is possible that many fuel cell systems may be furnishing power to the power grid. For safety reasons, the fuel cell systems may be designed to shut down or at least disconnect from the power grid when the main utility that supplies power to the power grid shuts down. This scheme permits servicing of the power grid when the main utility shuts down by ensuring that all sources of power to the grid are removed from the grid.
For purposes of detecting when the main utility shuts down, a particular fuel cell system may monitor the voltage on the grid. In this manner, when the grid voltage decreases below some predefined threshold voltage, the fuel cell system may shut down in response to detecting this decrease. It is possible that the utility may lower the grid voltage when the overall load on the grid approaches the capacity of the grid. Such a lowering of the grid voltage, however, may cause the fuel cell systems to shut down, as the voltage drop may inadvertently indicate a shut down of the main utility to these fuel cell systems.
Thus, there is a continuing need for an arrangement and/or technique to address one or more of the problems that are stated above.
In an embodiment of the invention, a technique includes coupling a generator to a power grid to provide power to the power grid. A scheme is used to detect a shut down of the power grid, and the generator is prevented from providing power to the power grid in response to the detection of the shut down of the power grid. An indication is received to modify the scheme, and the scheme is modified based on the indication.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.